1. Field
Exemplary embodiments of the present invention relate to a semiconductor memory device, and more particularly, to memory and a memory system including an address storage circuit.
2. Description of the Related Art
A memory cell of a memory includes a transistor configured to act as a switch and a capacitor configured to store a charge (data). The data is distinguished between ‘High’ (logic 1) and ‘Low’ (logic 0) depending on whether a charge is present in the capacitor, that is, whether the capacitor has a high terminal voltage.
In principle, the charge should remain in the capacitor and retention of data should not consume power. However, data may be lost because the initial charge stored in the capacitor is reduced due to the current leakage attributable to the PN junction of a MOS transistor. In order to prevent the loss of data, data within a memory cell is read before it is lost and the capacitor is recharged to a normal level based on the read information. This operation is periodically repeated in order to maintain the data. The process of recharging cells to retain data is called a refresh operation.
FIG. 1 is a diagram showing part of a cell array in order to describe word line disturbance. In FIG. 1, ‘BL’ denotes a bit line.
In FIG. 1, ‘WLK−1’, ‘WLK’, and ‘WLK+1’ denote word lines arranged in parallel in the cell array. The word line WLK indicated by ‘HIGH_ACT’ is a word line that has been activated a large number of times or has had a high frequency of activation, and the word lines WLK−1 and WLK+1 are adjacent to the word line WLK. ‘CELL_K−1’, ‘CELL_K’, and ‘CELL_K+1’ denote memory cells coupled to the respective word lines WLK−1, WLK, and WLK+1. The memory cells CELL_K−1, CELL_K, and CELL_K+1 include respective cell transistors TR_K−1, TR_K, and TR_K+1 and respective cell capacitors CAP_K−1, CAP_K, and CAP_K+1.
In FIG. 1, when the word line WLK becomes activated and precharged (or deactivated), voltages of the word lines WLK−1 and WLK+1 rise and fall attributable to a coupling phenomenon generated between the word line WLK and the word lines WLK−1 and WLK+1. The amount of charge stored in the cell capacitors CAP_K−1 and CAP_K+1 is influenced. Accordingly, if the word line WLK is greatly activated-precharged and thus the word line WLK oscillates between an active state and a precharge state, data stored in the memory cells CELL_K−1 and CELL_K+1 may be damaged or lost due to changes in the amount of charge stored in the cell capacitors CAP_K−1 and CAP_K+1.
Furthermore, due to an electromagnetic wave that is generated when a word line oscillates between an active state and a precharge state, electrons may move to and from a cell capacitor coupled to an adjacent word line and data stored in the memory cell may be damaged or lost.